1. Field of the Invention
The present invention relates to an apparatus for attaching a boot to a ski and more specifically relates to a safety binding for cross-country skiing.
2. Description of the Prior Art
Numerous apparatus are known which hold the front end of the boot on the ski, while allowing the heel to be lifted during skiing . The only movement possible in these apparatus is the lifting of the heel of the boot to permit skiing.
During skiing, to ensure the effective guiding of the ski by the skier, the front of the boot must be held with sufficient rigidity. As the rigidity with which the boot is held in the lateral direction across the foot increases, the ability of the skier to guide the ski becomes more precise. However, there are disadvantages to rigidly holding the boot to prevent lateral pivoting. In addition, such a binding creates great risks for the skier who does not possess a great technical facility in skiing and who does not ski with maximal ease and safety. These novice skiers ski in such a manner that their feet must make torsion movements relative to the ski, in order to avoid fractures. However, if their feet are held with a high degree of lateral rigidity, they cannot make these torsional movements necessary to avoid injury.
To overcome this problem safety-release bindings have been proposed that either allow a simple release of the boot from the ski or allow torsional movement of the boot relative to the ski without the release of the boot. German patent No. 2907365, German Utility Model No. 7723934, and French patent No. 8100358 are examples of these safety-release bindings.
According to various embodiments of these bindings, the binding is mounted on the ski so as to be adapted to rotate around a real vertical journal axis or around a virtual axis, formed by the cooperation of a section of a projection and a section of a groove. The pivoting axis is either placed under the front end of the boot as seen in FIG. 1 or in front of the boot, as seen in FIG. 2. Although this is an improvement over bindings that do not pivot, the location of the pivoting axis is not correct, and has serious shortcomings for the following reason. During skiing, either during the propulsion phase, during the duck walking phase, or even during descent, the action of the boot creates a force at the bottom of the foot, a distance from the pivot axis (denoted by F in FIGS. 1 and 2). This force F causes torsional movement of the boot which results in the lateral rotation and the release of the binding when the leg is not exposed to dangerous torsional forces. Thus, untimely releases of the boot will occur. The skier, to prevent these untimely releases and to improve the quality of his skiing is forced to increase the release threshold of the locking system that maintains the boot against lateral pivoting. However, this increased threshold does not allow the release of the boot when dangerous torsionazl movement occurs so that the binding is rendered completely ineffective when it is necessary to prevent injury to the leg.